Tree swallows are migratory birds commonly found across North America. They are small sleek birds only about five inches in length and weighing just under one ounce. Though they are known to migrate long distances from Central America to Canada, they have been seen in some parts of California throughout the year.
The Sea and Sage Audubon Society in Irvine, California has established a program to monitor the tree swallows and their nests at the San Joaquin Wildlife Sanctuary. The site is owned by the Irvine Ranch Water District and functions as a water reclamation facility as well as a wildlife sanctuary. Nestboxes, which are small wooden boxes on posts that resemble traditional birdhouses, are strategically placed along the edge of the ponds throughout the area. The water is an essential resource for the birds because it attracts many of the insect species they need for food.
Biologist Christine Tischer heads up the nestbox monitoring program for Sea and Sage Audubon. She began getting involved in the project in 1999 and now helps keep track of more than 100 nestboxes on the property. Along with a team of fellow volunteers, she makes frequent visits to the nestboxes to document the progress of the birds.
“They are not endangered or threatened in any way. But that makes for a good study bird because they are so prevalent, and they do readily adapt, and they are in large numbers. So, we can get a lot of information fast, versus when you have an endangered species where you only have one pair to study, and you don't want to harass them,” says Tischer. “That would be the importance of this program. It's not necessarily saving the species from the brink of extinction, but it's helping gather information for other birds,” she adds.
Much of the data collected is shared with the Golondrinas de las Americas community of researchers studying swallows, which is based out of Cornell University in Ithaca, New York. Methods used to monitor the birds include analyzing nests size and quality, measuring the wings and heads of chicks, weighing them, and attaching numbered bands to the chicks’ legs before fledging occurs. The number on the band can help researchers determine information like age and where the bird was born.
Habitat loss due to development is one of the biggest challenges the birds face. Many of the old trees with readily available nest cavities have been removed. Tree swallows cannot excavate their own nest cavities. So, they rely on using holes left by other birds like woodpeckers; Sometimes they’ll even use old cliff swallow burrows. The nestboxes provide a much-needed resource for them in the absence of these natural cavities, allowing them to successfully nest and raise chicks.
The nestbox program appears to be working. The researchers get a chance to obtain important data about the birds and, ultimately, the health of the local ecosystem. The tree swallows, which at one point were rare in Orange County as a breeding species, are now abundant. Many bluebird nestboxes in the area now have tree swallows regularly using them as well. In addition to the success seen in Orange County, Tischer says, “San Diego didn't have any tree swallows nesting. And now they're all the way down to the border. So, they're really flourishing because of this program.”
Tischer welcomes people of all ages to get involved if they’re interested in helping the birds. She says the best way to volunteer is through the Sea and Sage Audubon website.